Sloped or overhead glazing systems generally include a plurality of horizontal framing members or purlins and vertical framing members or rafters interconnected to form a structural framing grid which provides a plurality of glazing openings into which architectural panels, e.g. glass panels, are secured. The framing grid is attached to a building superstructure. The grid usually has a slope or pitch of about 15.degree. to about 75.degree. as measured from the horizontal plane of the superstructure. Typically, each purlin and each rafter consists of two primary parts, one on the inside of the panels and one on the outside of the panels. The primary parts are interconnected to form glazing recesses or pockets adapted to receive and retain marginal edge portions of the panels. Various forms of connector and sealing components are employed to secure the panels within the glazing pockets and to minimize infiltration of moisture, air, dust, and other elements, from the outside to the inside of the glazing pockets. Typical sealing components comprise resilient sealing gaskets which grip the inner and outer panel surfaces. The tightening force applied to the connector components to interconnect the inside and outside primary parts of the purlins and rafters compressively biases the panel gripping gaskets against the inside and outside panel surfaces to securely retain the glazing panels within the framing grid and to minimize penetration of moisture, air, and the like into the glazing pockets and the building interior. However, if water, e.g. rain water and/or window washing water, leaks past the outside sealing gaskets and builds up in the glazing pockets, then columnar water pressure may force the water around the inside sealing gaskets and into the building interior, which may cause damage to the building interior and/or objects contained therewithin.
Presently available glazing systems provide facilities for collecting and draining moisture which penetrates past the outside sealing gaskets into the glazing pockets. U.S. Pat. No. 4,448,001 issued to Whitmeyer et al. teaches a moisture dam system for vertical curtain walls which includes insertion of vertical dams near the ends of the horizontal frame members to prevent discharge of water accumulated in the horizontal members through the ends of the horizontal members and into other zones of the curtain wall frame system. The collected water is discharged through weep openings provided in the horizontal members to the outside of the curtain wall. U.S. Pat. No. 3,719,014 discloses a similar moisture control system for curtain walls, employing end cap members for the horizontal members rather than the inserted vertical dams. U.S. Pat. Nos. 4,448,001 and 3,719,014 suffer common disadvantages. First of all, if the water builds up in the horizontal members faster than it can be discharged therefrom, then the water will exert pressure against and eventually leak past the interior sealing gaskets and into the building interior. Secondly, no provisions are made to handle water buildup within the vertical frame members and glazing pockets. U.S. Pat. No. 4,055,923 issued to Biebuyck teaches the use of water diverters mounted internally of the horizontal mullions of a curtain wall framing system for diverting intruding water to exit points on the exterior sides of the mullions. At the crossings of vertical and horizontal mullions, internal diverter bridge pieces connect the water diverters of adjacent horizontal mullions to thereby divert water from the vertical mullions to the horizontal mullion diverter network. A disadvantage of this water diversion system is that the combined water which infiltrates the vertical and horizontal mullions is diverted through just the horizontal mullions. If the water builds up within the horizontal mullions faster than it can be discharged therefrom, then the water will exert pressure against and eventually leak past the interior sealing gaskets into the building interior.
U.S. Pat. Nos. 4,114,330 and 4,070,806 teach sloped curtain wall or skylight systems wherein gutters integral to the framing members (e.g. the rafters) function to collect some of the infiltrating moisture and moisture which may result from condensation within the framing members or on the surfaces of the glass panels due to changes in atmospheric pressure and/or temperature. The collected moisture is directed along the gutters which extend continuously over the length of the rafters and/or purlins and into a sill member disposed at the bottom of the sloped curtain wall. The accumulated moisture collected from the framing members by the gutters is then discharged from the sill member to the outside of the building wherein the curtain wall is installed. A drawback of the moisture control system of these sloped curtainwall systems is that both condensate moisture and infiltrating moisture are collected and discharged in a common moisture control system, thereby requiring a greater sill discharge capacity. Further, if the accumulated moisture builds up faster than the capacity of the sill member to discharge it to the outside, then the moisture may form a water column within the gutters. The water column exerts pressure on the inside sealing gaskets and some water eventually leaks past the sealing gaskets and into the building interior. Another shortcoming of these moisture control systems is that some moisture is allowed to pass into the glazing pockets, with the consequence that if discharge of the moisture is not rapid enough, the moisture will form a column of water within the glazing pockets which may, like the standing water in the gutter network, leak past the inside sealing gaskets and into the building interior. The problem of water buildup is more pronounced in multi-story installations and when the pressure within the framing system is less than the outside atmospheric pressure, as the negative pressure draws moisture into the framing system.
It would therefore be advantageous to have a sloped glazing system having an internal drainage system which precludes the possibility of moisture buildup in the glazing pockets and which provides systematic, separate zonal collection and drainage of infiltrated and condensate moisture.